Forensic expert Police Colonel Johan Vermeulen also said he thought Mr Pistorius had hit the door with the bat from a low angle, indicating he was not wearing his prosthetic legs at the time.

At the scene

By Pumza FihlaniBBC News, Pretoria

A big day in the Oscar Pistorius murder case. The defence worked tirelessly to disprove a finding by Colonel Johan Vermeulen, a decorated forensic expert in the South African Police Service (SAPS).

Oscar Pistorius's toilet door stood obtrusively in the courtroom, held up by a white frame, behind it a toilet cubicle. Col Vermeulen, a state witness, told the court that based on the marks on the door and their level Mr Pistorius was on his stumps when he struck the door with a cricket bat.

The defence strongly challenged his version, adding that they will present their own expert witness who will prove Mr Pistorius was in fact wearing his prosthetics. Defence lawyer Barry Roux also introduced another dimension to the case, suggesting that the police recklessly handled the crime scene - he pointed to police shoe prints on the door. The forensics from the scene are a make or break for either side.

Mr Roux's plan seems to include discrediting the integrity of the evidence collection process. He has already hinted at the possible contamination of the crime scene, placing the SAPS under a rather embarrassing spotlight.

This contradicts the athlete's claim that he had been wearing his artificial limbs.

Correspondents say whether or not the athlete was on his prosthetic limbs is important because it could match parts of his story that he accidentally shot Ms Steenkamp, or expose inconsistencies in it.

The damaged toilet door, with four bullet holes, was examined in the courtroom along with a replica of the toilet cubicle.

Forensic evidence on the location from which shots were fired, how they were grouped and their trajectory were presented to the court on Wednesday.

Cross-examining, Mr Pistorius' defence team asked forensic expert Col Vermeulen to kneel and lift his feet, which caused him to wobble.

The defence team claimed that Mr Pistorius therefore would not have been able to balance on his stumps and break down the door using a cricket bat.

Defence lawyer Barry Roux also alleged that police had contaminated the crime scene by stepping on the door.

Col Vermeulen argued that if Mr Pistorius was balanced enough to fire a gun, he could also break down a door with a bat.

The forensics expert argued that the angle and location of the marks on the door suggested that they had been caused by someone much shorter than him.

The defence team argued that a mark on the bottom of the door showed where Mr Pistorius had tried to kick open the door using his prosthetic legs. Col Vermeulen agreed that this was possible.

Oscar Pistorius passed several notes to his lawyers throughout the testimony

"The marks on the door are actually consistent with him not having his legs on and I suspect they must be similar to the height that he was when he fired the shots," he told the court.

The prosecution argues that Mr Pistorius hit the door with the cricket bat before the shots were fired, but the defence claims it was the other way round.

The trial is now halfway through its second week.

Fabricated evidence

Earlier on Wednesday, a friend of Mr Pistorius claimed that the star had driven at 200 km/h (124mph) and that he had taken a picture of the speedometer to prove it.

The defence team alleged that Darren Fresco was himself driving at the time and had therefore fabricated evidence.

On Tuesday, Mr Pistorius' defence team questioned a pathologist's finding that his girlfriend had eaten less than two hours before he killed her.

This contradicts the athlete's account that the pair had been in bed for several hours before the shooting.

Oscar Pistorius shot Reeva Steenkamp through a bathroom door

The state is seeking to convince the court that Mr Pistorius and Ms Steenkamp, a 29-year-old model, and reality TV star, had an argument before the athlete fired the shots that killed her.

There are no juries at trials in South Africa, and his fate will ultimately be decided by the judge, assisted by two assessors.

If found guilty, the 27-year-old, a national sporting hero dubbed the "blade runner", could face life imprisonment.